Abstract: A conventional media filter such as a gravity sand filter is converted into a membrane filter. The media is removed and replaced by immersed membrane modules. Transmembrane pressure is created by a static head pressure differential, without a suction pump, thereby creating a membrane gravity filter (MGF). Preferred operating parameters include transmembrane pressure of 5-20 kPa, 1-3 backwashes per day, and a flux of 10-20 L/m2/h. The membranes are dosed with chlorine or another oxidant, preferably at 700 minutes*mg/L as Cl2 equivalent per week or less. The small oxidant does is believed to provide a porous biofilm or fouling layer without substantially removing the layer. The media filter may be modified so that backwash wastewater is removed from near the bottom of the tank rather than through backwash troughs above the membrane modules. Membrane integrity testing may be done while the tank is emptied after a backwash.

Abstract: A conventional media filter such as a gravity sand filter is converted into a membrane filter. The media is removed and replaced by immersed membrane modules. Transmembrane pressure is created by a static head pressure differential, without a suction pump, thereby creating a membrane gravity filter (MGF). Preferred operating parameters include transmembrane pressure of 5-20 kPa, 1-3 backwashes per day, and a flux of 10-20 L/m2/h. The membranes are dosed with chlorine or another oxidant, preferably at 700 minutes*mg/L as Cl2 equivalent per week or less. The small oxidant does is believed to provide a porous biofilm or fouling layer without substantially removing the layer. The media filter may be modified so that backwash wastewater is removed from near the bottom of the tank rather than through backwash troughs above the membrane modules. Membrane integrity testing may be done while the tank is emptied after a backwash.

Abstract: A conventional media filter such as a gravity sand filter is converted into a membrane filter. The media is removed and replaced by immersed membrane modules. Transmembrane pressure is created by a static head pressure differential, without a suction pump, thereby creating a membrane gravity filter (MGF). Preferred operating parameters include transmembrane pressure of 5-20 kPa, 1-3 backwashes per day, and a flux of 10-20 L/m2/h. The membranes are dosed with chlorine or another oxidant, preferably at 700 minutes*mg/L as Cl2 equivalent per week or less. The small oxidant does is believed to provide a porous biofilm or fouling layer without substantially removing the layer. The media filter may be modified so that backwash wastewater is removed from near the bottom of the tank rather than through backwash troughs above the membrane modules. Membrane integrity testing may be done while the tank is emptied after a backwash.

Abstract: A conventional media filter such as a gravity sand filter is converted into a membrane filter. The media is removed and replaced by immersed membrane modules. Transmembrane pressure is created by a static head pressure differential, without a suction pump, thereby creating a membrane gravity filter (MGF). Membrane permeate passes through a bed of adsorption media optionally located in a tank with the membrane modules. The membranes are backwashed periodically with permeate, which bypasses the adsorption media as it returns to the membrane module.

Abstract: A conventional media filter such as a gravity sand filter is converted into a membrane filter. The media is removed and replaced by immersed membrane modules. Transmembrane pressure is created by a static head pressure differential, without a suction pump, thereby creating a membrane gravity filter (MGF). Preferred operating parameters include transmembrane pressure of 5-20 kPa, 1-3 backwashes per day, and a flux of 10-20 L/m2/h. The membranes are dosed with chlorine or another oxidant, preferably at 700 minutes*mg/L as Cl2 equivalent per week or less. The small oxidant does is believed to provide a porous biofilm or fouling layer without substantially removing the layer. The media filter may be modified so that backwash wastewater is removed from near the bottom of the tank rather than through backwash troughs above the membrane modules. Membrane integrity testing may be done while the tank is emptied after a backwash.

Abstract: A filtration process has permeation periods and deconcentration periods. The length of the permeation period or periods between backwashes is chosen, or controlled, to allow the system to reach a TMP and flux value at which the system is operating near its mechanical limits.

Abstract: Modules of ultrafiltration or microfiltration membranes are arranged in a tank open to the atmosphere to substantially cover the cross sectional area of the tank. A filtration cycle has permeation steps and deconcentration steps. During permeation, supply of feed substantially equals feed removed and little if any aeration is used. During deconcentration, aeration with scouring bubbles is provided with one or both of backwashing and feed flushing. In feed flushing, feed water is supplied to the tank from below the modules. Excess tank water created during deconcentration flows generally upwards through the modules and out through a retentate outlet or overflow at the top of the tank.

Abstract: Modules of ultrafiltration or microfiltration membranes are arranged in a tank open to the atmosphere to substantially cover the cross sectional area of the tank. A filtration cycle has permeation steps and deconcentration steps. During permeation, supply of feed substantially equals feed removed and little if any aeration is used. During deconcentration, aeration with scouring bubbles is provided with one or both of backwashing and feed flushing. In feed flushing, feed water is supplied to the tank from below the modules. Excess tank water created during deconcentration flows generally upwards through the modules and out through a retentate outlet or overflow at the top of the tank.

Abstract: An element for use in ultrafiltration or microfiltration of potable water has a large number of small diameter hollow fibre membranes attached between two headers. Side plates attached to the sides of the headers define vertical flow channels containing the membranes. The elements may be placed side by side and stacked on top of each other to form cassettes having continuous vertical flow channels through the entire cassette. The membrane modules or cassettes may be arranged to cover a substantial part of the cross sectional area of an open tank. Tank water may flow upwards or downwards through the flow channels. A tank may be deconcentrated by at least partially emptying and refilling the tank with fresh water while permeation continues. Excess tank water created during deconcentration may flow generally upwards through the modules and out through a retentate outlet or overflow at the top of the tank.

Abstract: Modules of ultrafiltration or microfiltration membranes are arranged in a tank open to the atmosphere to substantially cover the cross sectional area of the tank. A filtration cycle has permeation steps and deconcentration steps. During permeation, supply of feed substantially equals feed removed and little if any aeration is used. During deconcentration, aeration with scouring bubbles is provided with one or both of backwashing and feed flushing. In feed flushing, feed water is supplied to the tank from below the modules. Excess tank water created during deconcentration flows generally upwards through the modules and out through a retentate outlet or overflow at the top of the tank.

Abstract: Modules of ultrafiltration or microfiltration membranes are arranged in a tank open to the atmosphere to substantially cover the cross sectional area of the tank. A filtration cycle has permeation steps and deconcentration steps. During permeation, supply of feed substantially equals feed removed and little if any aeration is used During deconcentration, aeration with scouring bubbles is provided with one or both of backwashing and feed flushing. In feed flushing, feed water is supplied to the tank from below the modules. Excess tank water created during deconcentration flows generally upwards through the modules and out through a retentate outlet or overflow at the top of the tank.

Abstract: A method of filtering a feed of water to provide potable water includes adding a coagulant to the water to be filtered to encourage the formation of flocs. About 0.1 to 1 mg/L of a polymeric flocculation aid is also added to the water to be filtered to further encourage the formation of flocs. Some of the flocs may then removed from the water to be treated, for example with a clarifier. A filtered permeate is removed from the water to be treated with a membrane filtration device. The membrane filtration device may be an immersed suction driven membrane filtration device. The polymeric flocculation aid may be added to the body of water in a dosage between about 0.2 and 0.5 mg/L. The dosage of the polymeric flocculation aid may also be approximately equal to the dosage which gives the minimum turbidity of the water to be treated, for example, as determined by jar testing.

Abstract: An apparatus for treating water has a contact zone, a separation zone and a collection zone. The contact zone and the separation zone are located adjacent to each other in a tank. Feed water containing pressurized dissolved air enters and releases bubbles into the separation zone. The bubbles contact the contaminants to form bubble-contaminant complexes that float upwards and spread over the surface of the tank. Bubble-contaminant complexes move to the collection zone. A filtered permeate is withdrawn from the water in the tank through an immersed membrane filtration module located within the separation zone of the tank.

Abstract: A method of filtering a feed of water to provide potable water includes adding a coagulant to the water to be filtered to encourage the formation of floes. About 0.1 to 1 mg/L of a polymeric flocculation aid is also added to the water to be filtered to further encourage the formation of flocs. Some of the flocs may then removed from the water to be treated, for example with a clarifier. A filtered permeate is removed from the water to be treated with a membrane filtration device. The membrane filtration device may be an immersed suction driven membrane filtration device. The polymeric flocculation aid may be added to the body of water in a dosage between about 0.2 and 0.5 mg/L. The dosage of the polymeric flocculation aid may also be approximately equal to the dosage which gives the minimum turbidity of the water to be treated, for example, as determined by jar testing.

Abstract: An element for use in ultrafiltration or microfiltration of potable water has a large number of small diameter hollow fibre membranes attached between two headers. Side plates attached to the sides of the headers define vertical flow channels containing the membranes. The elements may be placed side by side and stacked on top of each other to form cassettes having continuous vertical flow channels through the entire cassette. The membrane modules or cassettes may be arranged to cover a substantial part of the cross sectional area of an open tank. Tank water may flow upwards or downwards through the flow channels. A tank may be deconcentrated by at least partially emptying and refilling the tank with fresh water while permeation continues. Excess tank water created during deconcentration may flow generally upwards through the modules and out through a retentate outlet or overflow at the top of the tank.

Abstract: A method of chemically cleaning normally immersed suction driven filtering membranes involves backwashing a chemical cleaner through the membranes while the tank is empty in repeated pulses in which the chemical cleaner is pumped to the membranes separated by waiting periods in which chemical cleaner is not pumped to the membranes. The duration and frequency of the pulses is preferably chosen to provide an appropriate contact time of the chemical, preferably without allowing the membranes to dry between pulses and without using excessive amounts of chemical. In other aspects, such membranes preferably used for filtering water to produce potable water in a batch process are backwashed with a chemical cleaner substantially at the same time as the tank is being drained. The chemical cleaner is optionally supplied in pulses.

Abstract: In an apparatus for providing a continuous integrity test for suction driven filtering membrane assemblies 10, a monitoring line 32 diverts a portion of permeate to a monitoring device 30 (e.g. a turbidimeter). Both ends 34, 36 of the monitoring line are connected to the permeate pipe 20 upstream from the permeate pump 26 and at points of relatively higher and lower pressures respectively, to cause fluid to flow through the monitoring line. The relatively higher and lower pressures may be caused by a source of head loss 38 (e.g. a valve) in the permeate line. The source of head loss may be adjusted to provide a required flow through the monitoring device by a control 43 communicating with a flow meter 42 in the monitoring line. Membrane assemblies may be individually monitored although many of them may be connected to a common permeate pump (FIG. 2).

Abstract: A method of chemically cleaning normally immersed suction driven filtering membranes involves backwashing a chemical cleaner through the membranes while the tank is empty in repeated pulses in which the chemical cleaner is pumped to the membranes separated by waiting periods in which chemical cleaner is not pumped to the membranes. The duration and frequency of the pulses is preferably chosen to provide an appropriate contact time of the chemical, preferably without allowing the membranes to dry between pulses and without using excessive amounts of chemical. In other aspects, such membranes preferably used for filtering water to produce potable water in a batch process are backwashed with a chemical cleaner substantially at the same time as the tank is being drained. The chemical cleaner is optionally supplied in pulses.